IMHO, deciding between Cuba and Maui and Roratonga is like trying to decide between Chinese or Italian for dinner.
I guess the things you want to consider are what do you want to do on your vacation? Sit on a beach and sip on drinks with little umbrellas? Do you want to immerse yourself with culture? Do you want to go scuba diving? If so do you care about what you want to see? ... these are the sorts of things you'll need to weigh in on.
Cuba - cheap, warm, beaches, resort experience. Underwater - good snorkeling, decent reefs, Caribbean reefs (ie., no clams, no Nemo's in anemones. Lots of gorgonians though - Caribbean reefs are quite pretty in that aspect).
Hawaii - easy to get to, no language barrier, no need to stay at an all-inclusive resort (ie., I'd much rather just rent a condo myself, cook my own meals, and just do my own thing). TONNES to see and do outside of beaches. Ie., on Maui alone, the drive up to Hana is one of the most picturesque drives you can do on this planet. Hale'akala crater is out of this world. Good snorkeling and dive opportunities, but the reefs are not the same as what you'll find further south.
Roratonga- grass roofs huts on stilts over the water, South Pacific reefs to see. If I could do anything or go anywhere, I myself would go here out of the 3 options listed here. But bear in mind I would be spending as little time as possible outside of the water.
To just have a "warm beach vacation" where the intent is just de-stress, chill out with a drink with an umbrella, then somewhere closer and cheaper will do. But to see Reefs (with a capital "R"
) then yeah, plan to go further south. I haven't seen too many reefs but I have seen the Great Barrier Reef and I have seen Hawaiian reefs and I have seen Carribean reefs and I have to say - once you have seen the south Pacific reefs, you'll know what I mean - they're in a whole different category.
That's my take anyhow.
I hope I'm not making the choice more difficult..